1. Field of the Invention
This invention relates to an internal thread forming apparatus, more particularly to an internal thread forming apparatus which rotates a tap in one direction when actuating a rotary lever, and in the opposite direction when letting go of the rotary lever.
2. Description of the Related Art
Because a conventional internal thread forming apparatus is normally used in association with the cutter feeding device of a machine tool, the precision of the internal thread forming apparatus is reduced. To increase precision, it is necessary for an internal thread forming apparatus to be provided with a built-in tap feeding device. It is understood that the higher the rotational speed of a tap, the smaller the torsion of the tap used for forming an internal thread. The rotational speed of the rotatable main shaft of the machine tool is too high to allow a conventional internal thread forming apparatus to produce a wide size range of internal thread. For example, it is difficult for a conventional internal thread forming apparatus to produce internal threads of more than a 16 mm-diameter. Accordingly, it is necessary to install a rotational speed reduction device in an internal thread forming apparatus in order to increase the torsion of the tap.